quote- [ If you filled an aircraft tire to about 150 PSI (some tires are inflated to over 200 psi) with normal air on the ground it could easily double at altitude and blow the tire up with catastropic results.

Uhh, I don't think so That kind of defies the laws of physics dose'nt it? The tire may tend to expand a tiny bit because the outside pressure will decrease but the pressure inside the tire can not increase unless you add more air, increase the temperature or decrease the size of the tire. In fact on a hot day, or most any day, the pressure would drop slightly instead of increasing because of the drastic temperature drop between ground level and 30,000 ft. I agree with you about the heat generated on landing but pressure increase with altitude? No way! I picked about 30,000 ft as an example because I assume you are talking about jets and plain air is of no concern at all in my Cessna 152 which will never see over 12,000 ft but lots of aircraft use plain air and go a hell of a lot higher than that without tire problems. As has already been pointed out Oxygen depletion would be of no concern in a paint booth or any painting area because ventilation is required anyway, like I said earlier the paint fumes and over-spray would reach toxic and blinding levels long before Oxygen depletion becomes a problem.

holy crap oldred, the service ceiling of a cessna 152 is 12,000 at best. density-altitude usually = a lot less. i never had mine over much more than 6000'. are you wiley post re-incarnated... come back to earth and keep posting all those welding threads. don't leave, we all need you..

Is Co2 as flammable as nitrogen? I read somewhere that it was..
(all kinds of disinformation out there....cain't never be too sure of what ya read)

Yes, CO2 is a flammable as N2. Both are considered non-flammable. For that matter, both are used to suppress fire in one way or another.

And this is why you have to be extremely careful around either of them. Basically, our body oxidizes food using the O2 from the atmosphere. In essence, we are doing a "slow burn" in order to live. N2 and CO2 have a tendency to displace the O2 in the atmosphere, thus preventing our slow burn. No O2, no life. Hard to enjoy a nice paint job in that state.

Maybe you are thinking of H2 (the gas, not the vehicle). Think Hindenburg.

Mikey, in the early days of VOC rules (after the "Clean air act" of 1990 in Ca) the equipment manufacture did EVERYTHING to try to make a system to beat it. "Throwing" the paint on with an airless was just one of them. They even thought that some day we would be applying the finish in a big applique vinyl sheet! Then they figured that the auto manufacture would paint the parts and we wouldn't even have the rights to paint.

The early HVLP guns were a living hell! And the equipment was just the beginning, how about the products? HOLY HELL, they just DROPPED the solvents out, that was their solution to the problem, no VOC in the product, no VOC problem. HOLY CRAP, they made the friggin crappiest junk to work with ever. And this was dumped on us in just a few years. Lacquer was dropped, urethanes were "new", it was hell.

But after all is said and done, there are some damn good products out there and damn good equipment to apply it.

holy crap oldred, the service ceiling of a cessna 152 is 12,000 at best. density-altitude usually = a lot less. i never had mine over much more than 6000'. are you wiley post re-incarnated... come back to earth and keep posting all those welding threads. don't leave, we all need you..

Never said I have had it that high, That little Lycoming sure would be doing some gasping but we like to think big don't we?

Is the nitrogen being used on the planes that fly higher? I mean, REALLY on all of them? What was the big difference when they weren't using it? For that matter, when were they just using air, when did it change?

It's a heat issue.
C/P
The reason airlines and race car crews fill their tires with nitrogen has absolutelly nothing to do with rate-of-loss or oxidation or even fuel economy. Nitrogen expands and contracts at a lesser rate with changes in temperature than atmospheric air. The process of separating the nitrogen out for the tanks used in this process removes the moisture content in normal air. It is the presence of moisture that causes the noticable increase in tire pressure with temperature increase. This is a BIG deal when you cruise at 200mph for 500 laps and you need all the traction you can get (meaning keeping the pressure as low as regulations allow).

It makes a big difference on airlines for massive planes coming into land where tire temperatures skyrocket rapidly. Again, keeping expansion down gives the pilots better traction, hence better control, during the rollout.

It's a heat issue.
Nitrogen expands and contracts at a lesser rate with changes in temperature than atmospheric air.

There would be NO change in internal tire pressure due to a decrease in atmospheric pressure. There would be a slight increase in the DIFFERENCE between internal and external pressure due to the fact that atmospheric pressure would be less at altitude, but even this would most likely be more than offset due to the drastic drop in temperature that occurs at higher altitudes. As far as using Nitrogen to control pressure on aircraft tires it very well could make a difference on landing with all that heat build-up and the point about the moisture content in regular compressed air makes a lot of sense.

Ok so I figure I should get this right since I started it with erroneous info, so I did a bit of research. Nitrogen offers the advantage of being dry, inert (does not support combustion), and does not damage the tire inner liner. It is also stable with temp change which is a big concern in aviation. Not in a cessna as that is not much different than a car, but in airliners, fast jets, heavy transport.

As for my comment about expansion at altitude I have no idea why I said that. Even though there is a difference in pressure at altitude the tires internal volume of gas will not change, regardless of the gas inside. The pressure differential would increase and the tire would 'grow' as altitude increases but it wouldn't matter what gas is inside as to how much growth you would have. Due to the construction of the tire it would probably be negligible.

Speede, There must be some big advantage to using Nitrogen, I have noticed that several outfits now offer Nitrogen tire inflation outfits that are quite spendy, don't know why someone who wanted to use it could not just use a tank of compressed Nitrogen and a regulator it would be a heck of a lot cheaper? Nitrogen (using a tank and regulator) is used on suspension struts on large off road haul trucks and the same equipment used to charge these could easily fill tires since it is just a simple regulator, hoses and fittings. Since these struts are partially filled with oil they would certainly diesel under load and shock if regular air was used so it is understandable why they use Nitrogen but I have never seen it used in the tires of these big rigs though, maybe it would be a good idea? The sales pitch for those tire filling rigs (I think even Harbor Freight has one!) claims substantially longer tire life and increased fuel mileage so maybe it is something that will soon become common.

We use it on tires, struts, hydraulic ressvoirs and accumulators. We use bottles but I know that when I was in the military we had a few nitrogen generators. Very expensive back then. As they are becoming more common the cost may become more business friendly but even with our volume we can't justify anything but bottles. Mind you our bottles are in a cart with a regulator/booster that is worth 5g's or so. If nitrogen is that much better for tires I would imagine trucking fleets would benefit from it's use. How long does a tire last before it gets chucked these days. I've never heard of a problem with inside tire wear (how many times can you recap a tire) so I would suspect the big gain is stable tire pressures which give better, more consistent gas mileage. On the stock car after just 25 laps our tires pressures can rise 15-20% using air.

Fundamentally, air, oxygen and nitrogen will all behave exactly the same, in terms of just how much pressure will change for each 10 degrees of temperature change. However, temperature alone is not the whole story. Ambient air contains moisture, which nitrogen does not. If moisture is there, it contributes to a greater change in pressure, simply because at lower temp, water condenses to become a liquid. A liquid form of water occupies very little volume and contributes only a negligible pressure to the tire. But at higher temp, water becomes a gas; water evaporates inside the tire as temperature rises. With ambient air, which contains about 20.9% oxygen, the oxygen permeates through the rubber of the tire, so some leaks out. With nitrogen, containing only a little residual oxygen, pressure changes due to oxygen loss are greatly reduced. So, on both counts, the race car guys are correct; nitrogen is more predictable - nitrogen is dry; it has no moisture to contribute extra pressure changes with temperature. And nitrogen permeates out much slower than oxygen, so pressure changes due to that leakage are almost eliminated, compared with ambient air.

As the link says all gases expand at the same rate so you will see the same increase in Pressure with a measured increase in temp. for air as Ni. (or for any mix of gases for that matter).

“But at higher temp, water becomes a gas; water evaporates inside the tire as temperature rises.”
If water becomes a gas then it behaves exactly as the other gases including Ni, they say that in the first sentence. With regards to moisture content in the tire can someone explain to me how water vapor that expands less than or the same as a gas can affect the total volume/pressure of a tire when it occupies less than 1% of the total gas in the tire. This reasoning has been mentioned a few times in this thread. If you believe this and want a gas that is dry and behaves exactly like Ni fill your tires up with the same air you spray paint with. No moisture, no problems.

“And nitrogen permeates out much slower than oxygen, so pressure changes due to that leakage are almost eliminated, compared with ambient air.”
How is the leakage of a few molecules of air going to affect a tire in a few hours of a race? (Even if this is true your talking about such a small amount of time difference it is probably incalculable).

Keep in mind this web site is put there by the people selling Ni. I think the Ni theory for road vehicles should be on the same shelf as the rest of the snake oil products that the auto industry seems to be saturated with.

I have yet to read a decent explanation as to why it is advantageous to use Ni in car tires.

I have no clue. I have never sprayed a car. You're the expert - you should be telling us!

Sounds expensive though.

Edit - Brian -- You know I am serious about that. I am tired of being told by companies trying to sell their products what is true or false. It is up to people who know what they are talking about (like yourself) to debunk these myths and stop people wasting their hard earned cash on crap. Thank god for forums and the internet, if you look hard enough you will always find the truth. (Also thank you Jon for all your hard work on your powerTV detective work)

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